Fixed line number generator

Updated the line number chunk regex to match an edge case. Added test cases to confirm the fix.

Here's an example:
```diff
diff --git a/html/exp2.txt b/html/exp2.txt
index a78cb18..e2274ae 100644
--- a/html/exp2.txt
+++ b/html/exp2.txt
@@ -1 +1 @@
-assome example text
+asassome example text
```